1. Field of Art
The present invention relates to a film transporting mechanism for cameras.
More particularly, the invention relates to a film transporting mechanism for self-developing (instant-picture) cameras.
2. The Prior Art
Self-developing cameras are known per se. They utilize a film pack cassette having a housing which is provided in one of its major wall surfaces with a film exposure window. A stack of individual film sheets is located in the housing and biased towards the exposure window by a spring or the like. After an exposure, during which the film sheet closest to (i.e., immediately behind) the exposure window is exposed to scene light, the just-exposed film sheet is expelled from the housing through a slot in one of its endwalls, thus placing the next (subjacent) film sheet in position for exposure.
Since the film sheets are of the self-developing type they must not only be transported, but the developer (contained in a pouch of each film sheet) must be squeezed out and spread over the exposure area of the film sheet. To effect these functions, a pair of nip rollers is provided which are so located that when the camera is loaded with a film pack the discharge slot of the latter becomes positioned adjacent to the nip. After exposure the film sheet is then expelled through the discharge slot until its leading end enters the nip of the rollers; thereafter, the rollers (one or both of which are of course driven) transport the film sheet further and, during its passage through the nip, the developer is squeezed and spread due to the pressure exerted by the rollers.
Two different types of such film packs are known, both operating on the principle outlined above. Both of these types have cassette housings which are provided with a special slot through which a gripper of the camera film transporting mechanism engages a lateral edge of the respectively uppermost film sheet to push the film sheet into the nip of the transport and developer rollers (hereafter called "transporting rollers" for simplicity).
Because the gripper exerts asymmetrically acting forces upon the film sheets (it engages only one lateral edge), the prior-art arrangements are not always able to shift the film sheets properly (and in proper orientation) into the nip of the transporting rollers. One problem that is encountered, is that the film sheet being shifted tends to be pressed against the sidewall of the cassette with its lateral edge that is opposite to the one engaged by the gripper; this of course results in transporting difficulties.